The invention relates generally to wavelength division multiplexed optical communication systems, and more particularly, to a modular, all-optical cross-connect that may be employed in wavelength division multiplexed optical communication systems.
Wavelength division multiplexing (WDM) has been explored as an approach for increasing the capacity of fiber optic networks to support the rapid growth in data and voice traffic applications. A WDM system employs plural optical signal channels, each channel being assigned a particular channel wavelength. In a WDM system, signal channels are generated, multiplexed, and transmitted over a single waveguide, and demultiplexed to individually route each channel wavelength to a designated receiver. Through the use of optical amplifiers, such as doped fiber amplifiers, plural optical channels are directly amplified simultaneously, facilitating the use of WDM systems in long-distance optical systems.
Recently, switching elements that provide a degree of reconfigurability have become available. These reconfigurable optical elements can dynamically change the path along which a given wavelength is routed to effectively reconstruct the topology of the network as necessary to accommodate a change in demand or to restore services around a network failure. Examples of reconfigurable optical elements include optical Add/Drop Multiplexers (OADM) and Optical Cross-Connects (OXC). OADMs are used to separate or drop one or more wavelength components from a WDM signal, which is then directed onto a different path. In some cases the dropped wavelengths are directed onto a common fiber path and in other cases each dropped wavelength is directed onto its own fiber path. OXCs are more flexible devices than OADMs, which can redistribute in virtually any arrangement the components of multiple WDM input signals onto any number of output paths. FIG. 1 shows a conventional cross-connect 100 that has two input ports 1011 and 1012 and output ports 1031 and 1032, which can each communicate a WDM signal having N channels or wavelengths xcex1-xcexN. Each WDM input and output port is coupled to a demultiplexer and multiplexer, respectively. Specifically, cross-connect 100 includes demultiplexers 1051 and 1052, and multiplexers 1071 and 1072. Cross-connect 100 also includes Mxc3x97M switching fabric 109, where M is equal to N times the number of WDM input/output ports (m). In the example shown in FIG. 1, M is equal to 2N. Switching fabric 109 is traditionally an electronic switching core such as a digital cross-connect, however for current high capacity optical systems this is being replaced with an optical switching system.
Unfortunately, because current OXC""s optical switches have a relatively high insertion loss, they require optical-to-electrical interfaces and regenerators into and out of the cross-connect. While these regenerators overcome the problem of insertion loss and effectively allow wavelength conversion of the signal as it traverses the switching fabric, they substantially add to the cost of an already expensive switching fabric because a regenerator is required for each and every wavelength that is used in the network.
Another limitation of the aforementioned conventional OXC is that it is difficult to increase the number of input and output ports when such additional capacity is needed sometime after the OXC is initially installed and operational. In order to provide such modularity, the switching fabric 109 as initially installed must include its maximum anticipated capacity, because otherwise the loss and number of connections increase too rapidly. In other words, it is impractical to provide an Mxc3x97M switching fabric that is itself modular. This limitation may be mitigated to a small degree by packaging demultiplexers and monitoring detectors outside the Mxc3x97M switching fabric in modules that can be installed incrementally, but since the switching fabric is the most expensive component in the OXC, the advantages of providing a conventional OXC that is modular are limited.
Accordingly, it would be desirable to provide a low-loss optical cross-connect in which modular functionality can be provided in a relatively easy and inexpensive manner.
In accordance with the present invention, an all-optical, optical cross-connect is provided, which includes first and second pluralities of multiport optical devices. Each of the first plurality of multiport optical devices have at least one input port for receiving a WDM optical signal and a plurality of output ports for selectively receiving one of more wavelength components of the optical signal. Each of the second plurality of multiport optical devices have a plurality of input ports for selectively receiving one of more wavelength components of the optical signal and at least one output port for selectively receiving one of more wavelength components of the optical signal. At least one of the first or second plurality of multiport optical devices are all-optical switches that can route every wavelength component independently of every other wavelength component. The plurality of input ports of the second plurality of multiport optical devices are optically coupled to respective ones of the plurality of output ports of the first plurality of multiport optical devices.
In accordance with one aspect of the invention, both pluralities of multiport optical devices are all-optical switches that can route every wavelength component independently of every other wavelength component. Alternatively one of the plurality of multiport optical devices may be optical couplers.
In accordance with another aspect of the invention, the all-optical switch includes a plurality of wavelength selective elements that each select a channel wavelength from among the plurality of wavelength components received at the input port. A plurality of optical elements are respectively associated with the plurality of wavelength selective elements. Each of the optical elements direct one of the selected wavelength components selected by the associated wavelength selective element to any one of the output ports independently of all other channel wavelengths.
In accordance with yet another aspect of the invention, an all-optical, optical cross-connect is provided which includes a first set of m reconfigurable all-optical switches, where m is ∞ 3. Each of the reconfigurable switches have at least (m+1) prearranged ports for receiving one or more wavelength components of a WDM optical signal. The reconfigurable switches selectively directing any wavelength component from one of the prearranged ports to any of the remaining ones of the prearranged ports independently of every other wavelength component. A second set of m reconfigurable all-optical switches are also provided, which each have at least (m+1) particular ports for receiving one or more wavelength components of a WDM optical signal. The reconfigurable switches in the second set route any wavelength component from one of the particular ports to any of the remaining ones of the particular ports independently of every other wavelength component. Each of the prearranged ports of each reconfigurable switch in the first set of switches is optically coupled to a particular port of a different reconfigurable switch in the second set of switches.